Can I use PHP reserved names for my functions and classes?

No, you can't. Thank god.

Actually, while defining such a method results in a parse error, using it does not, which allows some kind of workarounds:

class A {
    function __call($method, $args) {
        if ($method == 'new') {
            // ...
        }
    }
}

$a = new A;
$a->new(); // works!

A related feature request dating back to 2004 is still open.

Edit January 2016

As of PHP 7, it is now possible to name your methods using keywords that were restricted so far, thanks to the Context Sensitive Lexer:

class Foo {
    public function new() {}
    public function list() {}
    public function foreach() {}
}

You still can't, however, name your class Case I'm afraid.

You can't do that, an alternative option is to just use _case() or _new() as the function names

Also check out:

Is it possible to "escape" a method name in PHP, to be able to have a method name that clashes with a reserved keyword?

By default it is not possible, they are reserved words and you can't use them.

http://www.php.net/manual/en/reserved.keywords.php

May be you can recompile PHP or something like this to achieve your aim, but I think (as the other people that answered you) that it is not a good idea :)

HTH!